1. Field of the Invention
The present invention relates to a technique of transmitting information between information processing devices such as computers. In particular, the invention relates to an information transmission technique using a portable information terminal device receiving information transmitted from a plurality of transmission devices.
2. Description of the Background Art
A system for transmitting geographic information to a mobile terminal device is one example of systems for communicating information between computers. As this type of system, there is a system for transmitting geographic information from a computer which stores geographical database to a mobile terminal device. Japanese Patent Laying-Open No. 6-120877 discloses a navigation system for transmitting navigation information based on position information of a mobile terminal device.
Referring to FIG. 1, this navigation system includes a center computer 700 generating voice guidance according to destination information received from a radio mobile station 500 via a radio base station 400, radio base stations 400, 410 and 420 connected to center computer 700 via a public circuit 600 and communicating by radio with radio mobile station 500 located in respective management zones 402, 412 and 422, and radio mobile station 500.
Radio mobile station 500 includes a circuit to be used by a travelling person for entering destination information, a circuit for transmitting the entered destination information to center computer 700 via radio base station 400, and a circuit for outputting voice guidance received from radio base stations 400, 410 and 412.
Center computer 700 includes: a geographical database; a voice guidance generating circuit connected to the geographical database and public circuit 600 for generating a first voice guidance for providing a route from a present position 404 to a way point 406 according to the destination information received from radio base station 400 that manages zone 402 including the present position 404, the present position of radio mobile station 500 recognized from position information of radio base station 400, and the geographical database; and a transmission circuit connected to the voice guidance generating circuit for transmitting the generated first voice guidance to radio mobile station 500 via radio base station 400. Center computer 700 further includes an in-zone signal reception circuit receiving from radio base station 410 that manages zone 412 including way point 406 a signal (in-zone signal) indicating presence of radio mobile station 500 in the zone including way point 406.
The voice guidance generating circuit includes a circuit for generating a second voice guidance giving a route from way point 406 to destination 408. The transmission circuit includes a circuit for transmitting the generated second voice guidance to radio mobile station 500 via radio base station 410.
According to this navigation system, radio mobile station 500 transmits destination information to center computer 700 via radio base station 400. The voice guidance generating circuit of center computer 700 generates, according to the destination information received from radio base station 400 and position information of radio base stations 400 and 410, the first voice guidance supplying a route from present position 404 to way point 406. The voice guide generating circuit of center computer 700 further generates the second voice guidance supplying a route from way station 406 to destination 408. The transmission circuit of center computer 700 transmits the generated first voice guidance and second voice guidance to radio mobile station 500 via radio base stations 400 and 410, respectively. The in-zone signal reception circuit of center computer 700 receives the in-zone signal of radio mobile station 500 from radio base station 410 that manages zone 412 including way point 406.
In this way, in accordance with the destination information and other information received via radio base station 400, the first voice guidance indicating a route from present position 404 to way point 406 is transmitted from center computer 700 to radio mobile station 500. The first voice guidance is output from radio mobile station 500. A user carrying radio mobile station 500 follows the first voice guidance and accordingly moves to zone 412 managed by radio base station 410. In accordance with the in-zone signal and the like of radio mobile station 500 received via radio base station 410, the second voice guidance indicating a route from way point 406 to destination 408 is transmitted to radio mobile station 500. Radio mobile station 500 outputs the second voice guide. A travel route 430 from present position 404 to way point 406 and further to destination 408 can consequently be provided from center computer 700 to radio mobile station 500 by means of the voice guidance. The navigation system thus provided enables the user to reach destination 408 even in an unfamiliar area.
However, since the voice guidance of this navigation system that is transmitted via radio base stations 400, 410 and 420 from center computer 700 to radio mobile station 500 is based on the geographical database of center computer 700 connected via public line 600, the voice guidance provides details to the same extent. In other words, even if radio mobile station 500 is approaching destination 408, more detailed information regarding surroundings of destination 408 for example is not provided.